94 BREEDING 



stood before the result of it is described. Plate I. 

 represents the result of a cross between two races 

 of peas which differ in the colour of their cotyledons. 

 The two races crossed only differed in respect of a 

 single characteristic — colour. Both the parent forms 

 happened to be round. Fig. 21 represents the result 

 of a cross between two races of peas which differ 

 only in the form of their cotyledons. Both the 

 parent forms happened to be yellow — but this is 

 not shown in the figure. In the cross about to be 

 described the parent forms differ in respect of both 

 the colour and the form of their cotyledons ; that is to 

 say, the results shown separately in Plate I. and Fig. 21 

 are shown together. There is nothing new in the 

 case we are about to deal with : it is merely two 

 cases which have already been considered separately, 

 in separate crosses, considered together in one cross. 

 Indeed, every detail of the result of the cross between 

 the yellow wrinkled and the green round can be pre- 

 dicted from the knowledge which we now possess of 

 the result of crossing a yellow with a green, and a 

 round with a wrinkled. Yellow is dominant to green 

 and round dominant to wrinkled ; the result, there- 

 fore, of crossing a yellow wrinkled with a green round 

 is a yellow round. This is shown in Plate III. ; the 

 yellow wrinkled race is represented by a group of 

 six peas to the (top) left of the picture, the green 

 round one by a group of eight peas to the (top) right. 

 The first hybrid generation is represented by five 

 yellow round peas between and a little below the 

 parent forms. 



